β-Lactotensin (β-LT: His-Ile-Arg-Leu) is an ileum-contracting peptide derived from residues No. 146-149 of bovine β-lactoglobulin. The ileum-contracting activity of β-LT was blocked by the NT1 antagonist SR48692. β-LT was selective for the neurotensin NT2 receptor while neurotensin was selective for the NT1 receptor. β-LT is the first natural ligand showing selectivity for the NT2 receptor. β-LT showed hypertensive activity after intravenous administration at a dose of 30 mg/kg in conscious rats, while neurotensin showed hypotensive activity. The hypertensive activity of β-LT was blocked by levocabastine (1 mg/kg, i.v.), an NT2 antagonist. SR48692, which blocked the hypotensive activity of neurotensin, had no effect on the hypertensive activity of β-LT. These results suggest that the hypertensive activity of β-LT is mediated by the NT2 receptor. It was concluded that the NT1 and NT2 receptors mediate the opposite effect on blood pressure.
2003 by Japan Society for Bioscience, Biotechnology, and Agrochemistry